This invention relates to a method of forming thin film patterns, particularly thin films such as metallic films, in the fabrication of integrated circuits.
Most present techniques in the formation of vacuum deposited thin metallic film patterns make the use of etching in the presence of etch-resist photoresist layers to provide the selected pattern. This, in effect, involves the traditional photoengraving or photolithographic etching process. However, with the continued miniaturization of semiconductor integrated circuits to achieve greater component density and smaller units in large scale integrated circuitry, the art is rapidly approaching a point where such photolithographic etching of deposited film may be impractical for providing the minute resolution required for the fine linework of metallization, particularly at metal thicknesses in the order of 8,000 A - 25,000 A, in such large scale integrated circuitry.
An alternative method for forming such metallization in large scale integrated circuitry, which is presently under consideration and use in the art, is commonly denoted by the term "expendable mask method", "lift-off method", or "stencil method". The following references are typical of those describing these known types of methods.
1. T. D. Schlaback et al, "Printed and Integrated Circuitry", pp. 352-352, McGraw-Hill, New York, 1963. PA1 2. K. C. Hu, "Expendable Mask: A New Technique for Patterning Evaporated Metal Films", Electron Packaging and Production, October 1967. PA1 3. M. Hatzakis, "Electron Resist for Micro-Circuit and Mask Production", Journal of The Electrochemical Society, Vol. 116, p. 1033, 1969. PA1 4. H. I. Smith et al, "A High-Yield Photolithographic Technique for Surface Wave Devices", Journal of The Electrochemical Society, Vol. 118, p. 821, 1971.
U.S. Pat. Nos. 3,849,136 and 3,982,943 are typical of patents directed to a lift-off method and structure for depositing thin films which avoid the "edge-tearing" problem by providing deposition masks with apertures having a negative slope or "overhang". Because of this overhang, when thin films, particularly metal films, are deposited over the structure and the remaining photoresist is removed by standard lift-off techniques, the "edge-tearing" problem is minimized. Both of these patents provide effective techniques for forming deposition masks with such "overhangs". However, they must use a series of depositions and etching steps in order to produce the final deposition mask with the desirable "overhang".